Learn the basics of Java enumeration type enum

Introduction to the basic usage of Java enumeration type enum

1. Definition of enumeration type

The enumeration type (enum) is the Java programming language A type in that allows you to create a set of constants with fixed values. Enumeration types are similar to classes in Java, but they have some key differences. First, enumeration types are final, which means they cannot be inherited. Secondly, an enumeration type can only have one instance, which means you cannot create multiple objects of the enumeration type.

The definition of enumeration type is as follows:

enum MyEnum {
  // 枚举常量
}

For example, we can define an enumeration type to represent the days of the week:

enum DayOfWeek {
  SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

2. Use of enumeration types

Enumeration types can be used in the following ways:

• As a method parameter or return value
• As the type of a variable
• As an array Element

For example, we can use the DayOfWeek enumeration type to define a method that returns the day of the week:

public DayOfWeek getDayOfWeek() {
  return DayOfWeek.MONDAY;
}

We can also use the DayOfWeek enumeration type to define a Variable that stores the day of the week:

DayOfWeek dayOfWeek = DayOfWeek.TUESDAY;

We can also use the DayOfWeek enumeration type to define an array that stores all the days of the week:

DayOfWeek[] daysOfWeek = {
  DayOfWeek.SUNDAY, DayOfWeek.MONDAY, DayOfWeek.TUESDAY,
  DayOfWeek.WEDNESDAY, DayOfWeek.THURSDAY, DayOfWeek.FRIDAY,
  DayOfWeek.SATURDAY
};

3. Enumeration Comparison of types

Enumeration types can be compared in the following ways:

• Use the == and != operators
• Use the compareTo() method

For example, we can use the == operator to compare the values ​​of two DayOfWeek enumeration types:

if (dayOfWeek1 == dayOfWeek2) {
  // do something
}

We can also use the compareTo() method to compare the values ​​of two DayOfWeek enumeration types Value:

int result = dayOfWeek1.compareTo(dayOfWeek2);
if (result == 0) {
  // do something
} else if (result > 0) {
  // do something else
} else {
  // do something else
}

4. Traversal of enumeration types

Enumeration types can be traversed in the following ways:

• Use for-each loop
• Use the Iterator interface

For example, we can use a for-each loop to traverse all values ​​of the DayOfWeek enumeration type:

for (DayOfWeek dayOfWeek : DayOfWeek.values()) {
  // do something
}

We can also use the Iterator interface to traverse the DayOfWeek enumeration All values ​​of enumeration types:

Iterator<DayOfWeek> iterator = DayOfWeek.values().iterator();
while (iterator.hasNext()) {
  DayOfWeek dayOfWeek = iterator.next();
  // do something
}

5. Precautions for enumeration types

When using enumeration types, you need to pay attention to the following points:

• Enumeration Constants of types are final, which means they cannot be modified.
• An enumeration type can only have one instance, which means you cannot create multiple objects of the enumeration type.
• Enumeration types can implement interfaces, but they cannot inherit other classes.
• Enumeration types can contain methods and fields, but they cannot contain constructors.

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